The present invention relates to a check valve interposed, for example, in a discharge passage of a fuel pump to be opened and closed by the hydraulic pressure of fluid.
In motor vehicles, the check valve is interposed in a fuel passage for feeding fuel from the fuel pump to an internal combustion engine, and is in an open position during operation of the engine by the hydraulic pressure of fuel and in a closed position after engine stop due to no hydraulic pressure. By interposing the check valve in the fuel passage, the hydraulic pressure in the fuel passage is maintained at a predetermined value even after engine stop to allow immediate supply of fuel to the engine at engine restart.
A typical check valve is discloses in Japanese document JP-B2 2775797. This check valve is formed with a valve hole through which fuel or fluid flows, and comprises a housing formed on the outer peripheral surface of the valve hole and having a valve seat, a valve element disposed in the valve hole to be movable between a valve closed position where the valve element makes close contact with the valve seat to close the valve hole and a valve open position where the valve element moves away from the valve seat in the downstream direction to open the valve hole, a coil spring having one end engaged with the valve element and for biasing the valve element toward the valve closed position, and a valve holder for movably holding the valve element in the valve hole and with which another end of the coil spring is engaged.
The valve element comprises a semispherical valve head and a rod supported in a slide hole of the valve holder. The valve head has a surface covered with a seal member and an outer periphery integrated with a flange.
With the above structure, when a fuel pump starts to discharge fuel, the hydraulic pressure of fuel operates on the valve head of the valve element, with which the valve element is urged to move in the valve open position against a biasing force of the coil spring. At the instant that the valve element opens the valve hole, the lift is small, providing higher flow velocity of fuel flowing through a clearance between the valve element and the surface of the valve hole. Then, a hydraulic-pressure reduction occurs once at the surroundings of the valve element. With the valve element lifted even slightly, the hydraulic pressure operates also on the flange of the valve element. Therefore, the valve element undergoes a great pressing force resulting from the hydraulic pressure, surely moving to the valve open position against a biasing force of the coil spring.
Specifically, if the area of the valve element on which the hydraulic pressure acts is small, the valve element cannot completely move to the valve open position, causing occurrence of its vibration or oscillation and reduction in the pump efficiency due to pressure loss of fuel. In order to prevent such inconveniences, Japanese document JP-B2 2775797 proposes to arrange a flange with the valve element to increase the area on which the hydraulic pressure acts, thus surely moving the valve element to the valve open position.